So-called pillow-top mattresses have become fashionable in recent years. Through the provision of gussets, one for each of the top and bottom panels, such mattresses are constructed to appear as though a comforter or pillow has been placed on a conventional mattress to provide a more luxurious and comfortable appearance. The gussets extend around the perimeter of the mattress and connect the side panels to top and bottom panels of the mattress cover.
Pillow-top mattresses are typically far more expensive to manufacture than conventional mattresses, because of the additional manufacturing steps required to incorporate the gusset into the structure of the mattress cover. In conventional mattresses, typically only one tape edge operation is required for each top and bottom panel. The top panel is secured to an adjacent edge of the side panel all the way around the perimeter of the mattress, and this seam is covered with a tape which is stitched to the fabric at the same time the top or bottom panel is joined to the side panel. Prior to this tape edge operation, the side, top and bottom panels of the mattress cover have been precut and sized. Any inaccuracies in cutting and sizing typically can be accommodated by the machine operator by adjusting the position of the fabric during the assembly of the mattress cover.
In the manufacture of pillow-top mattress covers, several additional steps are required, all of which are highly labor intensive. After preparation and cutting to size of the top, bottom and side panels, as in conventional mattresses, the gussets must be assembled and sewn into place. The gussets are each typically formed of a single piece of material which must first be folded to form two flaps which are then stitched together along the folded edge. Each piece of material in the gusset typically includes a layer of fabric wrapped about or secured to a layer of foam or other padding. Thereafter, in a subsequent step, a strip of flange material is secured to one flap of the gusset. The flange material is necessary for attachment of the top and bottom panels of the cover directly to the components of the inner spring frame. This flange material typically is a non-woven material having a high strength.
For each of the top and bottom panels of the mattress cover, one flap of the gusset is stitched to the perimeter of a layer of a liner material. This liner, typically a high strength non-woven material, and its attached gusset are then placed on top of the inner spring and held in place by securing the flange material to the inner spring using attachment devices, such as hog rings. Once the liner is fixed in place, the exterior panel is glued thereto on its undersurface. Thereafter, the mattress is closed by stitching the edge of one flap of the gusset to the edge of the exterior mattress panel and by stitching the edge of the other flap of the gusset to the edge of the exterior side panel using a conventional tape edge sewing machine.
This prior art technique necessitates a gluing step during the assembly of the top and bottom panel of the mattress cover. If the gusset is sewn directly to the panel using existing sewing machines, the stitch would pass all the way through the panel and be externally visible, a result which is highly undesirable. Existing blind stitch machines, which would accomplish the desired result with no externally visible stitch, were incapable of handling materials as thick as pillow-top panels, especially the very thick panels which recently have become popular. The liner to which the gussets are sewn is usually a very thin sheet of material which can be accepted by conventional chain stitch machines. Since this liner is fully concealed by the mattress cover, this conventional stitch is not visible once the mattress has been closed.
During the step of sewing and taping one flap of the gussets to their associated panels, often it is desired to miter the corners of the gusset for a more finished look. If the corners are not mitered, the machine operator must gather the material to accommodate the extra material at the corners. Unless the operator is particularly skilled, sometimes the result is a rather uneven look, since the mattress covers are unwieldy and difficult to maneuver around the corners.
In existing systems, where mitered corners are desired, the operator typically cuts an extended length of previously formed gusset material at measured locations where the corners of the cover are expected to be, and the mitered corner is formed on the gusset material before it is attached to the panel. However, due to the nature and construction of the mattress cover material and of the gusset material, often the gussets and panels shrink or change shape at differing rates if left to sit, thus somewhat altering the location of the pre-mitered corner on the gusset material with respect to the corner on the mattress panel. This change occurs more frequently when the gusset is manufactured well in advance of the date of assembly of the mattress cover. Since the mitered corners on the gusset are not aligned precisely with the corners of the mattress cover panel, an accommodation has to be made by the operator at the time the gusset is attached to the mattress cover panel, such as by gathering the material or stretching where necessary to properly position the mitered corner. This adjustment results in extra operator time, as well as the possibility that the mitered corner is not properly positioned, or that the corner exhibits an uneven or undesired appearance. Even where the operator is able to properly position the mitered corner, the required stretching or gathering of the material produces a mattress cover which does not have the desired look and which might not be acceptable to all purchasers.
As can be seen, the prior art process for producing a pillow-top mattress cover requires many sewing steps, each of which must be manually controlled. Also, because of the large number of steps, greater opportunities exist for errors and for the production of mattress covers which are not uniform in look or which do not meet specifications. Finally, because existing blind stitch machines cannot sew gussets to mattress cover panels, a gluing step has become an accepted necessary practice in the industry. There are a number of drawbacks to gluing. It requires the introduction of a gluing step into the assembly process requires additional machinery and additional workers. Also, provision must be made for proper ventilation and removal of the fumes from the glue. The result is additional plant costs, which serve to increase the overall cost of manufacture.
There are several reasons why existing blind stitch machines are not suitable for making mattress covers. In the first place, typically only a bottom feed is provided, which comprises a roller or a pair of rollers which pulls the material through the stitching zone. In existing machines, this bottom feed is positioned behind the needle with respect to the direction of movement of the work. Thus, when the work is first introduced into the stitching zone, there is no positive feed until the stitching process has proceeded sufficiently far to allow the feed to grip the lower surface of the work being stitched. Also, because the feed is located behind the needle or stitching zone, when it is used with a large piece of work, such as a mattress cover, and when the mattress cover is rotated to accommodate a corner, the work occasionally breaks loose from the feed, requiring the operator to manually feed or move the work around until it again is engaged by the feed. This produces an uneven result, requires more operator attention, and could result in operator injury.
Secondly, most blind stitch machines presently available are not suitable for accommodating work as bulky and thick as a mattress cover panel. Existing blind stitch machines do not sufficiently press the thick fabric against the upper foot to allow the machine to produce the desired stitch. Also, the arm below the fabric cannot be pivoted sufficiently far out of the way to accept the work. Finally, the arm vibrates or bounces during sewing producing an uneven stitch.
It is therefore an object of the present invention to provide a method and apparatus for the assembly of pillow-top mattress covers which reduces the number of sewing steps and therefore reduces the cost of assembly.
It is a further object of the present invention to provide a method and apparatus for the assembly of pillow-top mattress covers which provides a more uniform result.
It is another further object of the present invention to design a blind stitch machine capable of being used for the assembly of pillow-top mattress covers.
It is yet another further object of the present invention to provide a method and apparatus for the assembly of pillow-top mattress covers which eliminates the need for a gluing step.